PC 2.1: locate and disconnect the SELV supply according to manufacturer specifications. The humble 12 V battery is the trigger of the whole HV system — it powers the ECUs that command the pack contactors closed. Disconnect the 12 V negative terminal (negative first, to avoid short-circuit sparks) and the contactors drop out, collapsing the external HV bus. But sequence and location matter: some vehicles hide the 12 V battery in the boot, under the rear seat or in a wheel arch; some require the ignition cycled off and the key removed to a distance of at least five metres first, because smart-entry systems can wake the car and re-close contactors. The OEM procedure is law here — it names the order, the terminal, the wait times and the warnings.